Integrated semiconductor devices are typically constructed en masse on a wafer of silicon or gallium arsenide. Each device generally takes the form of an integrated circuit (IC) die. If the die is to be encapsulated in a plastic package, it is first bonded to the die-mounting paddle of a leadframe which is attached to other leadframes in a leadframe strip. The wire attachment pads on the die are connected with their corresponding leads on the leadframe with aluminum or gold wire during a wire bonding process, following which the die is coated with a protective polyimide film. Finally, the die is encapsulated in plastic and the plastic-encapsulated chip undergoes a trim and form operation which separates the interconnected packages on the leadframe strip into individual entities and bends (forms) the leads of each package. The package is then recognizable as an IC "chip". The operation for manufacturing plastic-encapsulated packages is highly automated, allowing high quality and low cost.
IC packages take many forms, although the trend is clearly toward designs which increase mounting density. For years, the standard IC package was the dual-inline package or DIP. Such packages were typically through-hole soldered on printed circuit boards. A newer dual-inline lead design, known as small-outline J-lead package, has been rapidly supplanting the standard DIP design for two reasons. Firstly, the leads of an SOJ package are soldered to only one side of a circuit board, thus leaving the other side of the board free for the mounting of additional SOJ packages. Secondly, the leads are much less vulnerable to damage prior to board assembly, hence, there are fewer rejects. Both DIP and SOJ packages are horizontal packages (i.e., the die is mounted in a plane parallel to the board-attachment plane). Vertical packages are also coming into greater use because they permit greater circuit board mounting density. Vertical packages have a very narrow horizontal cross section, with the die mounted between the vertical sides of the package, the distance between which is minimized. All leads exit through the lower edge of the package. The zig-zag inline package or ZIP is a typical vertical package. A vertical package known as the zig-zag inline package or ZIP is also coming into greater use. Existing ZIPs are designed for through- hole-soldered connections on a circuit board. Since such packages require very little board area for connection, they are particularly useful where high-density applications are a must. Although the use of a surface-mount ZIP has been suggested by Barbara Cole of Boise, Idaho's Micron Technology, Inc., the appeal of such a package is greatly diminished by the requirement that each package be maintained in a vertical position over its associated mounting pads until a solder reflow operation is performed.
What is needed is a new type of package which combines the density advantages of both the SOJ-type package with the vertical packaging of the ZIP, which can be positioned on a circuit board with currently available board-stuffing equipment and which will maintain its vertical position on the board without auxiliary package-support apparatuses until final attachment of the package to the circuit board during a solder reflow operation.